NEW CU(III) PEROVSKITES - LA1-XYXCUO3 ESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.20) PREPARED UNDER OXYGEN-PRESSURE

New perovskites La1-xYxCuO3 (0 less-than-or-equal-to x less-than-or-eq ual-to 0.20) with trivalent copper have been prepared from La1-xYxCuO2 oxide as starting materials under high oxygen pressure conditions [70 kbar (7 GPa), 1300-degrees-C] using ''in situ'' the thermal decomposi tion of KClO3 in a belt-type reaction-cell. All stoichiometric oxides are characterized by a rhombohedral distortion of the perovskite struc ture. The oxygen stoichiometry is very sensitive to the preparation co nditions, in particular the structure of the reaction cell. Electric a nd magnetic properties underline a slight increase of the electronic l ocalization versus x in agreement with the small variation of the stru ctural distortion.